Emergency services were sent to the scene near the mouth of the River Moriston after reports that a woman had entered the water at around 1.30pm on Thursday, Aberdeen Coastguard said.
She was located and taken to Raigmore Hospital in Inverness by helicopter, where she died later.
Loch Ness RNLI lifeboat, coastguard teams and a coastguard helicopter were part of the operation.
Police, the fire service and the ambulance service were also involved.
Anyone with information should calls 101, quoting incident 1726 of May 3.